Danziger Oded, Shimon Liat, Horovitz Amnon
Department of Structural Biology, Wietzmann Institute of Science, Rehovot 76100, Isreal.
Protein Sci. 2006 Jun;15(6):1270-6. doi: 10.1110/ps.062100606. Epub 2006 May 2.
The ATPase activity of many types of molecular chaperones is stimulated by polypeptide substrate binding via molecular mechanisms that are, for the most part, unknown. Here, we report that such stimulation of the ATPase activity of GroEL is abolished when its conserved apical domain residue Glu257 is replaced by alanine. This mutation is also found to convert the ATPase profile of GroEL, a group I chaperonin, into one that is characteristic of group II chaperonins. Steady-state and transient kinetic analysis indicate that both effects are due, at least in part, to a reduction of the affinity of GroEL for ADP. This finding indicates that nonfolded proteins stimulate ATP hydrolysis by accelerating the off-rate of the ADP formed, thereby allowing more rapid cycles of ATP binding and hydrolysis.
许多类型分子伴侣的ATP酶活性会通过大多未知的分子机制被多肽底物结合所刺激。在此,我们报告,当GroEL保守的顶端结构域残基Glu257被丙氨酸取代时,对其ATP酶活性的这种刺激作用就会消失。还发现该突变会将I型伴侣蛋白GroEL的ATP酶谱转变为II型伴侣蛋白的特征性谱。稳态和瞬态动力学分析表明,这两种效应至少部分是由于GroEL对ADP的亲和力降低所致。这一发现表明,未折叠蛋白通过加速所形成ADP的解离速率来刺激ATP水解,从而允许ATP结合和水解的循环更快进行。